IEEE Spectrum October, 2016 - 57

the early-adopter blues

co nti n u e d f ro m pag e 4 8

even lure them back to land once they
reach the water. To protect the turtles,
the Florida Fish and Wildlife Conservation Commission now limits outdoor
lighting visible from sea turtle nesting
zones to amber, orange, and red wavelengths longer than 560 nanometers.
LEDs are fine, but only if they follow
this wavelength restriction.
A European Union-funded consortium called the Loss of the Night Network is supporting research on the
biological impact of LEDs and other
outdoor lighting. But well-controlled
ecological studies can take years of
painstaking observations, and at
the moment there is precious little
research on the impact of different
color spectra on wildlife.
In the meantime, human beings are
making their own displeasure known
based on health, environmental, and
quality-of-life concerns. Some residents
of Brooklyn, Seattle, and Houston have
joined the International Dark-Sky Association (IDA) in fighting installations of
blue-rich LED street lighting. And in
Canada, public outcry over the city of
Montreal's $84 million plan to replace
existing streetlights with LEDs centered
on light pollution and health impacts.
In response to questions that I posed
to the DOE about the early rollout of
blue-rich LEDs, the agency says it does
not recommend specific color temperatures for LED street lighting and that
it provides information about energy
efficiency ratings and color temperatures only to allow buyers to make
informed choices. Unfortunately, the
right choice is not always clear-just
months after the city of Davis, Calif.,
installed 4,000-K LED streetlights
in 2014, a high volume of complaints
prompted officials to spend $350,000
to replace 650 of those new lights with
less-efficient 2,700-K LEDs.
ED lighting manufact u re r s h ave t a ke n
notice of the public
rumblings about bluerich LEDs. This year
Cree, one of the top U.S. makers of LED
lighting, began offering 3,000-K LEDs

that could generate the same number
of lumens per watt as 4,000-K LEDs
(modern sodium lights have a color
temperature of 2,100 to 2,300 K).
Cree's breakthrough involved adding
a new high-efficiency red-emitting LED
to the standard blue LED with yellow
phosphors. As it turns out, producing
red light directly from the new LEDs
generates more lumens per watt than
adding red-emitting phosphors to the
standard yellow-emitting ones in a
white-light LED.
Erik Milz, Cree's vice president of
product marketing for outdoor lighting,
says the reddish LEDs give the warm
appearance of high-pressure sodium
lamps, but with the long lifetime and
high efficiency of LEDs. This technique
does not eliminate the blue but reduces
it; the DOE calculates that the output of
3,000-K LED lamps is about 20 percent
blue, compared with 30 percent for
4,000-K LEDs and 10 percent for highpressure sodium bulbs.
"Communities like the warmer light,"
says Patrick Roche, energy coordinator for the Boston-based Metropolitan
Area Planning Council. And 3,000 K is
good news for the IDA, which, along
with the Loss of the Night Network in
Europe and the American Medical
Association, recommends that color
temperature as the maximum.
The city of Tucson, with about a
billion dollars' worth of research
telescopes within 75 miles, is now
installing 3,000-K LEDs. And for Southern California, Monrad's consulting
firm is working on a regional streetlighting plan for a dozen communities
near the Palomar Observatory. The
upper limit for that project is 3,000 K,
but he is pushing for LEDs with a color
temperature of 2,700 K, a typical color
for an incandescent bulb.
Monrad has another design trick:
mixing LEDs of different colors in the
same fixture. He combined amber
LEDs with 3,000-K LEDs for a school
in southern Arizona. The white LEDs
switch off after workers go home, and
the amber lights switch on to provide
security with minimal impact on
astronomers and wildlife.

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Table of Contents for the Digital Edition of IEEE Spectrum October, 2016